1. Field of the Invention
The present invention relates to a double-sides playable disc player which can play back both sides of an information recording disc composed of a pair of circular base plates each having a signal recording layer, without turn-over of the disc once loaded.
2. Description of the Prior Art
Optical information recording discs such as video discs and DRAW (Direct Read After Write) discs contain information which is recorded as a multiplicity of minute depressions or pits produced by a laser beam spot. With such an optical information recording disc, it is important to protect a layer in which the pits are defined, i.e., a signal recording layer. One known arrangement for projecting a signal recording layer includes an optical information recording disc comprising a pair of circular base plates having respective signal recording layers, the circular base plates being coupled to each other with the signal recording layers inside.
FIG. 1 of the accompanying drawings fragmentarily illustrates a conventional double-sides playable disc player for playing back both sides of such an information recording disc without turn-over of the disc once loaded. FIG. 1 shows a disc clamp mechanism for clamping the disc on a turntable and a disc centering device for centering the disc with respect to the turntable. As shown in FIG. 1, the disc centering device comprises a centering member 4 axially slidably mounted on a drive shaft 3 of the turntable 2 and having a tapered surface 1 on an outer periphery thereof, a coil spring 5 disposed between the centering member 4 and the turntable 2, and a ring stopper 6 for retaining the centering member 4 on the drive shaft 3 against removal. The disc clamp mechanism includes a cup-shaped presser 8 rotatably mounted on a support member 12 by a ball 10 and a ball seat 11. The presser 8 can be brought into and out of engagement with an information recording disc 9 placed on the turntable 2 by vertical movement of the support member 12.
As described above, the disc 9 comprises a pair of circular base plates having respective signal recording layers 13, 14 and respective central holes and coupled to each other with the signal recording layers 13, 14 inside.
With the conventional double-sides playable disc player of the illustrated construction, the disc 9 can be centered with respect to the turntable 2 by placing the tapered surface 1 of the centering member 4 into the central hole of the disc 9 when the disc 9 is clamped on the turntable 2 by the disc clamp mechanism. Information can then be recorded on and reproduced from the signal recording layer of one circular base plate 13 by a recording/reproducing unit 16. Similarly, information can be recorded on and reproduced from the signal recording layer of the other circular base plate 14 by another recording/reproducing unit 17 without turning over the disc 9.
If the circular base plates 13, 14 joined to each other are displaced e from each other, then it may be possible to smoothly record information on and reproduce information from the signal recording layer of the circular base plate 13 held against the disc carrying surface of the turntable 2, but it may be difficult to smoothly record information on and reproduce information from the signal recording layer of the other circular base plate 14 since its central axis is displaced e from the center of rotation of the turntable 2.